Ultraviolet radiation causes methyl methacrylate polymers to deteriorate after as little as 100 hours of exposure. Ultraviolet radiation also tends to cause methyl methacrylate polymers to "yellow" which concomitantly reduces the ability of the methyl methacrylate to transmit ultraviolet radiation. Reduction in the ability of methyl methacrylate polymers to transmit ultraviolet radiation is a concern of the sunbed industry because this usually reduces the efficiency of the tanning process.
The art has attempted to address the degrading effects of ultraviolet radiation on methyl methacrylate by incorporating light stabilizers into these materials. For example, U.S. Pat. No. 4,550,136 adds sterically hindered amines(HALS) such as 2,2,6,6-tetramethyl-piperidine to the methyl methacrylate monomer prior to polymerization. Although the addition of (HALS) produces methyl methacrylate polymers with improved resistance to ultraviolet radiation, the addition of (HALS) is expensive.
The art has also attempted to improve the ultraviolet radiation resistance of acrylics by addition of propyl alcohol. As discussed in the article by A.S. Belichenkol et al, entitled "On the Mechanism of Polymer Destruction under UV and Gamma Irradiation: The Influence of Low Molecular Weight Additives Related to Vibrational Cross-Relaxation", Sixth Symposium on Radiation Chemistry, (1986), pages 535-538, polymer samples were prepared by bulk radical polymerization of monomer compositions of methyl methacrylate which incorporate about 5-20% propyl alcohol. The resultant polymers showed improved resistance to ultraviolet radiation for short exposures of about 100 hours. The large amounts of more than 5% propyl alcohol, however, would be expected to degrade the physical and mechanical properties of these polymers.
A need therefore exists to provide polymerized methyl methacrylate compositions which may be inexpensively manufactured and which show improved resistance to prolonged exposures to ultraviolet radiation without the need for addition of large amounts of additives.